Evidence for Intraflagellar Transport and Apical Complex formation in a Free Living Relative of the Apicomplexa

Source

Faculty of Veterinary Science, McMaster Building B14, University of Sydney, New South Wales 2006, Australia.

Abstract

Since its first description, Chromera velia has attracted keen interest as the closest free-living relative of parasitic Apicomplexa. The life cycle of this unicellular alga is complex and involves a motile bi-flagellate form. Flagella are thought to be formed in the cytoplasm, a rare phenomenon shared with Plasmodium in which the canonical mode of flagellar assembly, intraflagellar transport, is dispensed with. Here we demonstrate the expression of intraflagellar transport components in C. velia, answering the question of whether this organism has the potential to assemble flagella via the canonical route. We have developed and characterised a culturing protocol that favours the generation of flagellate forms. From this we have determined a marked shift in the mode of daughter cell production from two to four daughter cells per division as a function of time after passage. We conduct an ultrastructural examination of the C. velia flagellate form using serial TEM and show that flagellar biogenesis in C. velia occurs prior to cytokinesis. We demonstrate a close association of the flagellar apparatus with a complex system of apical structures including a micropore, conoid and a complex endomembrane system reminiscent of the apical complex of parasitic apicomplexans. Recent work has begun to elucidate the possible flagellar origins of the apical complex and in C. velia we show that these structures are contemporaneous within a single cell and share multiple connections. We propose that Chromera velia therefore represents a vital piece in the puzzle of the origins of the apical complex.

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The Toxoplasma Blog features the latest news regarding this protozoan parasite, including information about relevant scientific meetings and job opportunities. This blog is maintained by Bill Sullivan (wjsulliv[at]iu[dot]edu).